1. Field of the Invention
The present invention relates to a structure for high-density recording, and a process for producing the structure.
2. Description of the Related Art
Remarkable increase of the amount of information in recent years necessitates a higher recording density and a higher recording capacity for magnetic recording devices like a hard disk device (HDD). For the high recording density, magnetic particles contained in the recording layer should be micronized. However, the micronization of magnetic particles makes significant the thermal energy retained in the particle relative to the magnetic energy. This produces a superparamagnetic effect (thermal fluctuation) to cause dissipation of magnetic record disadvantageously. To stabilize the magnetic record against the thermal fluctuation, materials are being developed which have a higher magnetic anisotropy constant (Ku).
The magnetic recording medium containing a high-Ku material retains effectively the magnetization direction against an external magnetic field applied for recording. This lowers the sensitivity of the magnetic recording medium to an external magnetic field for the recording. In particular, a higher recording density and a higher data transfer rate demanded in recent years will limit the maximum intensity of the magnetic field generated by a recording head to make insufficient the recording capability. The recording magnetic field generated by a recording head depends on various factors including an electric current applied to the recording coil, a material and shape of the magnetic poles, a clearance between the head and the recording medium, and a soft magnetic underlayer (SUL). Therefore the intensity of the magnetic field in the recording head has an upper limit. The magnetic field generated by the recording head is expected to have an intensity of about 10 kOe at most. On the other hand, a recording medium which contains fine magnetic particles of about 5 nm and has a Ku of 107 erg/cm3 for resistance to thermal fluctuation, for example, is expected to require a magnetic field of 10 kOe or more for saturation of recording. Therefore, for further improvement of the recording density, not only the Ku as a recording medium characteristic but also the thermal fluctuation resistance should be improved.
A paper (IEEE. Transactions on Magnetics, 2003, vol. 39, no. 2, pp. 704-709) reports that the recording sensitivity can be improved by shifting the direction of the easy magnetization axis of the recording medium from the direction of the recording magnetic field of the head. Inclination of the easy magnetization axis direction of the recording medium by 45° from the magnetic field of the head recording enables decrease of the magnetic field intensity for magnetization reversal to a ½ level to increase the recording sensitivity while the thermal fluctuation resistance of the recording medium is retained.
Japanese Patent Application Laid-Open Nos. 2004-220671 and 2006-48864 disclose improvement of the recording sensitivity by controlling the easy magnetization axis direction. Specifically, Japanese Patent Application Laid-Open No. 2004-220671 discloses a recording medium having a constitution in which high-Ku nano-particles are dispersed in a low-melting matrix and the crystal axes of the nano-particles are inclined by 45° from the direction perpendicular to the recording medium face. Japanese Patent Application Laid-Open No. 2006-48864 discloses a discrete-track medium as a magnetic recording medium in which magnetic phase patterns partitioned by the grooves have respectively a taper inclined relative to the face perpendicular to the axis of crystal anisotropy of the magnetic phase.
On the other hand, for higher recording density of the magnetic recording medium, noises in record reproduction should be reduced beside the improvement in the thermal fluctuation resistance and in the recording sensitivity. For the noise reduction, exchange-coupling between the magnetic particles in the recording layer should be broken, and the magnetic particle size dispersion should be decreased to uniformize the magnetic cluster size. However, any of known techniques does not satisfy all of the above requirements.
The present invention intends to provide a structure for a recording medium or the like which comprises magnetic particles having controlled particle sizes and a high-Ku material having thermal fluctuation resistance. The present invention intends to provide also a process for producing the structure.